Pure nickel carbide (Ni C) nanoparticles with particle diameters of 40 nm have been prepared by thermal decomposition of nickel formate in the presence of oleic acid and oleyl amine. The co-existence of active nickel and active carbon plays an important role in the formation of metastable Ni C. Ni C powder decomposes at 770 K in an N atmosphere to yield nickel and carbon. While in an H atmosphere, Ni C powder is converted into Ni at 627 K. In addition, Ni C nanoparticles exhibit superparamagnetism and are easier to magnetize at room temperature due to their good crystallinity and few defects. Copyright © 2006 American Scientific Publishers All rights reserved.